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Acta Myologica • 2014; XXXIII: p. 1-12 



INVITED REVIEW 

Genetic basis of limb-girdle muscular 
dystrophies: the 2014 update 

ViNCENZO NiGRO AND MaRCO SaVARESE 

Dipartimento di Biochimica, Biofisica e Patologia Generate, Seconda Universita degli Studi di Napoli and Telethon Institute 

of Genetics and Medicine (TIGEM), Naples, Italy 



Limb-girdle muscular dystrophies (LGMD) are a highly het- 
erogeneous group of muscle disorders, which first affect the 
voluntary muscles of the hip and shoulder areas. The definition 
is highly descriptive and less ambiguous by exclusion: non-X- 
linked, non-FSH, non-myotonic, non-distal, nonsyndromic, and 
non-congenital. At present, the genetic classification is becoming 
too complex, since the acronym LGMD has also been used for a 
number of other myopathic disorders with overlapping pheno- 
types. Today, the list of genes to be screened is too large for the 
gene-by-gene approach and it is well suited for targeted next gen- 
eration sequencing (NGS) panels that should include any gene 
that has been so far associated with a clinical picture of LGMD. 
The present review has the aim of recapitulating the genetic ba- 
sis of LGMD ordering and of proposing a nomenclature for the 
orphan forms. This is useful given the pace of new discoveries. 
Thity-one loci have been identified so far, eight autosomal domi- 
nant and 23 autosomal recessive. The dominant forms (LGMDl) 
are: LGMDIA (myotilin), LGMD IB (lamin A/C), LGMDIC (ca- 
veolin 3), LGMDID (DNAJB6), LGMDIE (desmin), LGMDIF 
(transportin 3), LGMDIG (HNRPDL), LGMDIH (chr. 3). The 
autosomal recessive forms (LGMD2) are: LGMD2A (calpain 
3), LGMD2B (dysferlin), LGMD2C (y sarcoglycan), LGMD2D 
(a sarcoglycan), LGMD2E (p sarcoglycan), LGMD2F (6 sarco- 
glycan), LGMD2G (telethonin), LGMD2H (TRIM32), LGMD2I 
(FKRP), LGMD2J (titin), LGMD2K (POMTl), LGMD2L (anoc- 
tamin 5), LGMD2M (fukutin), LGMD2N (POMT2), LGMD20 
(POMTnGl), LGMD2P (dystroglycan), LGMD2Q (plectm), LG- 
MD2R (desmin), LGMD2S (TRAPPCll), LGMD2T (GMPPB), 
LGMD2U (ISPD), LGMD2V (Glucosidase, alpha ), LGMD2W 
(PINCH2). 

Key words: Limb-girdle muscular dystrophies, LGMD, NGS 

Introduction 

The term limb-girdle muscular dystrophy refers to a 
long list of Mendelian disorders characterized by a pro- 
gressive deterioration of proximal limb muscles. Very of- 
ten, other muscles are affected, together with the heart 



and the respiratory muscles. The clinical course and the 
expressivity may be variable, ranging from severe forms 
with rapid onset and progression to very mild forms al- 
lowing affected people to have fairly normal life spans 
and activity levels (1). The term LGMD is becoming de- 
scriptive and also comprises clinical pictures of different 
diseases. The original definition was given as muscular 
dystrophies milder that DMD and inherited as autosomal 
traits (2). However, the most severe forms with child- 
hood onset also result in dramatic physical weakness and 
a shortened life-span. The advent of next generation se- 
quencing approaches has accelerated the pace of discov- 
ery of new LGMD genes. Ten years ago the list included 
16 loci (3), while today the LGMD loci so far identified 
are thirty-one, eight autosomal dominant and 23 autoso- 
mal recessive. 

Autosomal dominant LGMD 

The LGMDl, i.e. the autosomal dominant forms, 
have usually an adult-onset and are milder, because affect- 
ed parents are usually in quite good health at reproductive 
age. They are relatively rare representing less than 10% 
of all LGMD. Sometimes, they correspond to particular 
cases of mutations in genes involved in other disorders, 
such as myotilin, lamin A/C or caveolin 3 (Table 1). 

LGMDIA - LGMDIA may be caused by mutations 
in the myotilin (MYOT) gene at chr. 5q31.2. The cDNA 
is of 2.2 kb and contains 10 exons. Myotilin is a Z-disk- 
associated protein. LGMDIA may be considered as an 
occasional form of LGMD (4). The first clinical report 
was in 1994 (5). The gene was identified in 2000 (6), but 
myotilin mutations have been rather associated with my- 
ofibrillar myopathy. LGMDIA is characterized by late 



Address for correspondence: Vincenzo Nigro, via Luigi De Crecctiio 7, 80 138 Napoli, Italy; Telethon Institute of Genetics and Medicine 
(TIGEM), via Pietro Castellino 111, 80131 Napoli, Italy. - E-mail: vincenzo.nigro@unina2.lt 



1 



Vincenzo Nigra and Marco Savarese 



Table 1. Autosomal dominant limb girdle muscular dystrophy. 



Gene 




Clinical phenotype 




Disease 


Locus 


Name 


Exons 


Prntpin 

(protein function) 


Typical 
onset 


Progression 


Cardiomiopathy 


sCK 


Allelic disorders (OMIM, #) 


LGMD1A 


5q31.2 


TTID 


10 


myotilin 


Adulthood 


Slow 


Not observed 


3-4X 


^^\/r^nc^th\/ m\/rifihrillQr T 
iviyu[Ja.ii ly, 1 [ lyui lui M icir , o 

(609200) 


(structural; Z disc) 


Myopathy, spheroid body 
(182920) 




















Cardiomyopathy dilated, 
1A(1 15200) 




















Charcot-Marie-Tooth 




















disease, type 261(605588) 




















Emery-Dreifuss muscular 




















dystrophy 2, AD(181350) 




















Emery-Dreifuss muscular 




















dystrophy 3, AR(181350) 




















Heart-hand syndrome. 










lamin A/C 
(structural; fibrous 
nuclear lamina ) 










Slovenian type(610140) 


LGMD1B 


1q22 


LMNA 


12 


Variable 
(4-38y) 


Slow 


Frequent 


1-6X 


Hutcfiinson-Gilford 
progeria( 176670) 


















Lipodystrophy, familial 
partial, 2(151660) 




















Malouf syndrome(21 21 1 2) 




















Mandibuloacral 




















dysplasia(248370) 




















Muscular dystrophy, 
congenital(613205) 




















Restrictive dermopathy, 
lethal(275210) 




















Cardiomyopathy, familial 
hypertrophic( 192600) 










caveolin 3 










Creatine phosphokinase, 
elevated serum( 123320) 


LGMD1C 


3p25.3 


CAV3 


2 


(scaffolding protein 
within caveolar 


Childhood 


Slow/ 
moderate 


Frequent 


10X 


Long QT syndrome 
y(bl lol o) 










membranes) 










Myopathy, distal, Tateyama 
type(b 14321 ) 




















Rippling muscle 
disease( 606072) 


LGMD1D 


7q36 


DNAJB6 


10 


DnaJ/Hsp40 
homolog, subfamily 
B, member 6 
(chaperone) 


Variable 
(25-50y) 


Slow 


Not observed 


MOX 






















Muscular dystrophy, limb- 
girdle, type 2R(615325) 










desmin (structural; 










Cardiomyopathy, dilated, 
1 1(604765) 


LGMD1E 


2q35 


DES 


9 


intermediate 
filament) 


Adulthood 


Slow 


Frequent 


5-1 OX 


Myopathy, myofibrillar, 
1(601419) 




















Scapuloperoneal 
syndrome, neurogenic, 
Kaesertype(181400) 


LGMD1F 


7q32 


TNP03 


23 


transportin 3 
(nuclear importin) 


Variable 
(1-58y) 


Slow/ 
moderate 


Not observed 


1-3X 












Heterogeneous 
nuclear 












LGMD1G 


4q21 


HNRPDL 


9 


ribonucleoprotein 
D-like protein 
(ribonucleoprotein, 
RNA-processing 
pathways) 


Variable 
(13-53y) 


Slow 


Not observed 


1-9X 




LGMD1H 


3p23-p25 








Variable 
(10-50y) 


Slow 


Not observed 


1-1 OX 





2 



Genetic basis of limb-girdle muscular dystrophies: the 2014 update 



onset proximal weakness with a subsequent distal weak- 
ness. Some patients show nasal and dysarthric speech. 
Serum CK is normal or mildly elevated. Muscle pathol- 
ogy shows rimmed vacuoles with or without inclusions. 
Electron microscopy shows prominent Z-line streaming. 
Cardiac and respiratory involvement occasionally occurs. 

LGMDIB - LGMDIB is also an occasional LGMD 
form caused by lamin A/C (LMNA) gene mutations at chr. 
Iq22 (7). The reference cDNA is of 3 kb and contains 12 
exons. The LMNA gene gives rise to at least three splic- 
ing isoforms (lamin A, C, lamin AAIO). The two main 
isoforms, lamin A and C, are constitutive components of 
the fibrous nuclear lamina and have different roles, rang- 
ing from mechanical nuclear membrane maintenance to 
gene regulation. The 'laminopathies' comprise different 
well-characterized phenotypes, some of which are con- 
fined to the skeletal muscles or skin, while others are 
multi-systemic, such as lipodystrophy, Charcot-Marie 
Tooth disease, progeroid syndromes, dilated cardiomyo- 
pathy and Emery-Dreifuss muscular dystrophy (EDMD). 
The LGMDIB is characterized by a symmetric proximal 
weakness starting from the legs, associated with atrioven- 
tricular conduction disturbances and dysrhythmias. CK 
is normal to moderately elevated. Most patients develop 
proximal leg weakness, followed by cardiac arrhythmias 
and dilated cardiomyopathy, with sudden death 20-30 
years later. However, there is a continuity between LG- 
MDIB and EDMD (8). Usually the more severe forms of 
EDMD with a childhood onset have missense mutations, 
whereas the milder LGMDIB is associated with het- 
erozygous truncating mutations: this may arise through a 
loss of LMNA function secondary to haploinsufficiency, 
whereas dominant-negative or toxic gain-of-function 
mechanisms may underlie the EDMD phenotypes. 

LGMDIC - LGMDIC is caused by mutations in the 
caveolin 3 gene {CAV3) at chr. 3p25.3. The CAV3 gene en- 
codes a 1.4kb mRNA composed of only two exons. Caveo- 
lin-3 is a muscle-specific membrane protein and the prin- 
cipal component of caveolae membrane in muscle cells in 
vivo: at present this is the only gene in which mutations 
cause caveolinopathies (9). LGMDIC is characterized by 
an onset usually in the first decade, a mild-to-moderate 
proximal muscle weakness, calf hypertrophy, positive 
Gower sign, and variable muscle cramps after exercise. 

LGMDID - Autosomal dominant LGMD mapped to 
7q36 has been classified as LGMD IE in OMIM, but as 
LGMDID in the Human Gene Nomenclature Committee 
Database. In the literature there is another LGMDID/E 
erroneously mapped to 6q, but we will use the acronym 
LGMDID for the 7q-disease and LGMDIE for the 6q- 



form. LGMDID is caused by heterozygous missense 
mutations in the DNAJB6 gene at chr. 7q36.3 (10). The 
reference cDNA sequence is 2.5kb-long, contains 10 ex- 
ons and encodes DnaJ homolog, subfamily B, member 
6. DNAJ family members are characterized by a highly 
conserved amino acid stretch (2) called the 'J-domain'. 
They exemplify a molecular chaperone functioning in 
a wide range of cellular events, such as protein folding 
and oligomeric protein complex assembly (11). Mis- 
sense heterozygous mutations of DNAJB6 (p.Phe89Ile, 
p.Phe93Leu and p.Pro96Arg) are all located in the Gly/ 
Phe-rich domain of DNAJB6 leading to insufficient clear- 
ance of misfolded proteins. Functional testing in vivo 
have shown that the mutations have a dominant toxic ef- 
fect mediated specifically by the cytoplasmic isoform of 
DNAJB6. In vitro studies have demonstrated that the mu- 
tations increase the half-life of DNAJB6, extending this 
effect to the wild-type protein, and reduce its protective 
anti-aggregation effect. 

DNAJB6 is located in the Z line and interacts with 
BAG3. Mutations in BAG3 are known to cause myofibril- 
lar myopathy (12). A characteristic pathological finding 
of LGMDID is the presence of autophagic vacuoles and 
protein aggregation. These protein aggregations contain 
DNAJB6 together with its known ligands MLFl and 
HSAPl, and also desmin, aB-crystallin, myotilin, and 
filamin C, which are known to aggregate in myofibrillar 
myopathy. These results suggest that the phenotype of 
LGMDID also overlaps with that of myofibrillar myo- 
pathy. 

LGMDID patients show mildly elevated serum CK 
levels. The lower limbs are more affected, particularly the 
soleus, adductor magnus, semimembranosus and biceps 
femoris. In contrast, the rectus femoralis, gracilis and sar- 
torius and the anterolateral lower leg muscles are mostly 
spared. DNAJB6 gene mutations may also be associated 
with distal-predominant myopathy. Symptoms in the up- 
per limbs appear later. Some patients develop calf hyper- 
trophy. Onset ranges from 25 to 50 years, with some pa- 
tients maintaining ambulation throughout life. No cardiac 
or respiratory involvement has been reported so far. The 
pattern of differential involvement could be identified at 
different stages of the disease process. 

LGMDIE - For the limb girdle muscular dystrophy 
originally linked to chr. 6q23 (13) we will use the name 
LGMDIE, even if it should be considered, more cor- 
rectly, as a form of autosomal dominant desminopathy or 
myofibrillar myopathy. This form is also known as dilated 
cardiomyopathy type IF (CMDIF). One family previous- 
ly categorized as having LGMD and dilated cardiomyo- 
pathy was reported, indeed, to have the splice site muta- 
tion IVS3-h3A>G in the desmin {DBS) gene at 2q35 (14). 



3 



Vincenzo Nigra and Marco Savarese 



For desmin see also LGMD2R. As in the desminopathies, 
LGMDIE family members show dilated cardiomyopathy 
and conduction defects together with progressive proxi- 
mal muscle weakness starting in the second or third dec- 
ade. Some family members had a history of sudden death. 
Serum creatine kinase is mildly elevated (150-350U/1). 
Muscle pathology may show dystrophic changes, but 
later the presence of abundant perinuclear or subsar- 
colemmal granulofilamentous inclusions have been also 
observed. The study of these inclusions by laser capture 
microdissection followed by mass spectrometry analysis, 
led to the identification of the disease-causing mutations 
in desmin (14). 

LGMDIF - LGMDIF was originally mapped to a 
3.68-Mb interval on chromosome 7q32.1-7q32.2 in a 
very large Italo-Spanish family. We presented the iden- 
tification of TNP03 by whole exome sequencing of four 
affected family members and the complete refining of the 
region at the WMS 2012. Data were then published (15): 
a frame-shift mutation in the transportin 3 (TNP03) gene 
is shared by all affected family members with 94% pen- 
etrance. The TNP03 gene is composed of 23 exons and 
encodes a 923 -amino acid protein, also expressed in skel- 
etal muscle. The frame-shifted TNP03 protein is larger 
than the wt, since it lacks the predicted stop codon and is 
found around the nucleus, but not inside. Patients with an 
onset in the early teens, show a more severe phenotype 
with a rapid disease course, while adult onset patients 
present a slower course. They have a prominent atrophy 
of lower limb muscles, involving especially the vastus lat- 
eralis and the ileopsoas muscle (16). Interestingly, some 
patients present with dysphagia, arachnodactyly and res- 
piratory insufficiency. CK range is l-3x. No cardiac in- 
volvement has been reported. 

LGMDIG - LGMDIG has been mapped to chr. 4q21. 
Very recently, the defect in the RNA processing protein 
HNRPDL has been identified (17) in two different families 
by whole exome sequencing. The HNRPDL gene contains 
8 exons and is ubiquiously expressed. The gene product is 
a heterogeneous ribonucleoprotein family member, which 
participates in mRNA biogenesis and metabolism. The 
reduced hnrpdl in zebrafish prodeces a myopathic pheno- 
type. Patients show late-onset LGMD associated with pro- 
gressive fingers and toes flexion Umitation (18). 

LGMDIH - By studying a large pedigree from 
Southern Italy, a novel LGMD locus has been mapped on 
chromosome 3p23-p25.1 (19). Most of patients present 
with a slowly progressive proximal muscle weakness, in 
both upper and lower limbs, with onset during the fourth- 
fifth decade of life. 



Autosomal recessive LGMD 

The autosomal recessive forms (LGMD2) are 
much more common, having a cumulative prevalence 
of 1:15,000 (2) with some differences among countries, 
depending on the carrier distribution and the degree of 
consanguinity. 

There are recessive genes in which the loss-of-function 
mutations on both alleles tipically result in a LGMD pheno- 
type (ordinary LGMD genes): they correspond to the first 
8 forms of LGMD2 (LGMD2A-2H) plus LGMD2L. On 
the contrary, other genes (occasional LGMD genes) show a 
phenotypic divergence with some mutations associated with 
LGMD and other ones determining a more complex disor- 
der. Specific variations in occasional LGMD genes cause the 
other forms (LGMD2I-2U). The best examples come from 
dystroglycanopathies in which the LGMD presentation is 
associated with milder alleles of genes mutated in congenital 
forms with brain involvement (Table 2). 

LGMD2A - LGMD2A is caused by Calpain 
3 (CAPN3) gene mutations and represents the most fre- 
quent LGMD worldwide (20, 21). The CAPN3 gene spans 
53kb of genomic sequence at chromosome 15ql5.2 and 
the transcript is composed of 24 exons encoding a 94kDa 
muscle-specific protein. There is a number of heterozy- 
gotes (1:100), carrying many different CAPN3 patho- 
genic changes. Calpains are intracellular nonlysosomal 
cysteine proteases modulated by calcium ions. A typical 
calpain is a heterodimer composed of two distinct subu- 
nits, one large (> 80 kDa) and the other small (30 kDa). 
While only one gene encoding the small subunit has been 
demonstrated, there are many genes for the large one. 
CAPN3 is similar to ubiquitous Calpain 1 and 2 (m-cal- 
pain and micro-calpain), but contains specific insertion 
sequences (NS, ISl and IS2). Calpains cleave target pro- 
teins to modify their properties, rather than "break down" 
the substrates. 

The phenotypic spectrum of calpainopathies is very 
broad, but they are true LGMD. For the clinical course, 
see also (1). 

LGMD2B - It is caused by missense or null alleles 
of the dysferlin (DYSF) gene (22). The DYSF gene spans 
233kb of genomic sequence at chr. 2pl3.2 and the major 
transcript is composed of 6,911 nt containing 57 exons 
in the HGVS recommended cDNA Reference Sequence. 
Dysferlin is an ubiquitous 230-KDa transmembrane pro- 
tein involved in calcium-mediated sarcolemma resealing. 
LGMD2B is the second most frequent LGMD2 form (15- 
25%) in numerous countries, but not everywhere (23). 
Muscle inflammation is recognized in dysferlinopathy 
and dysferlin is expressed in the immune cells. 



4 



Genetic basis of limb-girdle muscular dystrophies: the 2014 update 



Table 2. Autosomal recessive limb girdle muscular dystrophy. 



Gene 


Clinical phenotype 




Disease 


Locus 


Name 


Exons 


Protein product 


LGMD 
nhpnnt\/np 


Typical onset 


Progression 


Cardiomiopathy 


sCK 


Allelic disorders 
(OMIM, #) 


LGMD2A 


15q15 


CAPN3 


24 


Calpain 3 


ordinary 


Adolescence 


Moderate/ 


Rarely observed 


3-20X 




LGMD2B 


2p13.2 


DYSF 


56 


Dysferlin 


ordinary 


Young 
adulthood 


Slow 


Possible 


5-40X 


Miyoshi muscular 
dystrophy 1 (254130) 

Myopathy distal, with 
anterior tibial onset 
(606768) 


LGMD2C 


13q12 


SGCG 


8 


Y-Sarcoglycan 


ordinary 


Early chlldtiood 


Rapid 


Often severe 


10-70X 




LGMD2D 


17q21.33 


SGCA 


10 


a-Sarcoglycan 


ordinary 


Early childtiood 


Rapid 


Often severe 


10-70X 




LGMD2E 


4q12 


SGCB 


6 


fi-Sarcoglycan 


ordinary 


Early childhood 


Rapid 


Often severe 


10-70X 




LGMD2F 


5q33 


SGCD 


9 


6-Sarcoglycan 


ordinary 


Early childhood 


Rapid 


Rarely observed 


10-70X 


Cardiomyopathy dilated, 
1L (606685) 


LGMD2G 


17q12 


TCAP 


2 


Telethonin 


ordinary 


Adolescence 


Slow 


Possible 


10X 


Cardiomyopathy dilated, 
IN (607487) 


LGMD2H 


9q33.1 


TRIM32 


2 


Tripartite motif 
containing 32 


ordinary 


Adulthood 


Slow 


Not observed 


10X 


Bardet-Biedl syndrome 1 1 
(209900) 


LGMD2I 


19q13.3 


FKRP 


4 


Ful<utin related protein 


ordinary 


Late childhood 


Moderate 


Possible 


10-20X 




LGMD2J 


2q24.3 


TTN 


312or 
more 


Titin 


occasional 


Young 
adulthood 


Severe 


Not observed 


10-40X 


Cardiomyopathy, dilated, 
1G (604145) 
Cardiomyopathy, familial 
hypertrophic, 9(613765) 
Myopathy early-onset, 
with fatal cardiomyopathy 
(611705) 

Myopathy proximal, with 
early respiratory muscle 
involvement (603689) 

Tibial muscular dystrophy, 
tardive (600334) 


LGMD2K 


9q34.1 


P0MT1 


20 


Protein-O-mannosyl 
transferase 1 


occasional 


Childhood 


Slow 


Not observed 


10-40X 


Muscular dystrophy- 
dystroglycanopathy 
(congenital with brain and 
eye anomalies), type A, 1 
(236670) 

Muscular dystrophy- 
dystroglycanopathy 
(congenital with mental 
retardation), type B, 1 
(613155) 

Muscular dystrophy- 
dystroglycanopathy (limb- 
girdle), type C, 1 (609308) 


LGMD2L 


11p13-p12 


AN05 


22 


Anoctamin 5 


ordinary 


Variable (young 
to late 
adulthood) 


Slow 


Not observed 


M5X 


Gnathodiaphyseal 
dysplasia (166260) 

Miyoshi muscular 
dystrophy 3 (613319) 


LGMD2M 


9q31 


FKTN 


11 


Ful<utin 


occasional 


Early childhood 


Moderate 


Possible 


10-70X 


Cardiomyopathy, dilated, 
1X(611615) 
Muscular dystrophy- 
dystroglycanopathy 
(congenital with brain and 
eye anomalies), type A, 4 
(253800) 

Muscular dystrophy- 
dystroglycanopathy 
(congenital without mental 
retardation), type B, 4 
(613152) 



(continues) 



5 



Vincenzo Nigra and Marco Savarese 



Table 2. (follows). 



Gene 


Clinical phenotype 




Disease 


Locus 


Name 


Exons 


Protein product 


LGMD 
phenotype 


Typical onset 


Progression 


Cardiomiopathy 


sCK 


Allelic disorders 
(OMIM, #) 


LGMD2N 


14q24 


P0MT2 


21 


Protein-O-mannosyl 
transferase 2 


occasional 


Early ctiildtiood 


Slow 


Rarely observed 


5-15X 


Muscular dystrophy- 
dysfroglycanopathy 
(congenital with brain and 
eye anomalies), type A, 2 
(613150) 

Muscular dystrophy- 
dysfroglycanopathy 
(congenital with mental 
retardation), type B, 2 
(613156) 


LGMD20 


1p34.1 


POMGnTI 


22 


Protein 04inked 
mannose beta1,2"N- 
acetylglucosaminyl 
transferase 


occasional 


Late childfiood 


Moderate 


Not observed 


2-1 OX 


Muscular dystrophy- 
dystroglycanopathy 
(congenital with brain and 
eye anomalies), type A, 3 
(253280) 

Muscular dystrophy- 
dystroglycanopathy 
(congenital with mental 
retardation), type B, 3 
(613151) 

Muscular dystrophy- 
dystroglycanopathy (limb- 
girdle), type 0,3(613157) 


LGMD2P 


3p21 


DAG1 


3 


Dystroglycan 


singular 


Early ctiildtiood 


Moderate 


Not observed 


20X 




LGMD2Q 


8q24 


PLEC1 


32 


Plecfin 


singular 


Early ctiildtiood 


Slow 


Not observed 


10-50X 


Epidermolysis bullosa 
simplex with pyloric atresia 
(612138) 

Epidermolysis bullosa 
simplex, Ognatype 
(131950) 

Muscular dystrophy with 
epidermolysis bullosa 
simplex (226670) 


LGMD2R 


2q35 


DES 


9 


Desmin (structural; 
intermediate filament) 


occasional 


Young 
adulthood 




A-V conduction 
blocfc 


IX 


Muscular dystrophy limb- 
girdle, type 2R(615325) 

Cardiomyopathy dilated, 
11(604765) 

Myopathy myofibrillar, 
1(601419) 

Scapuloperoneal 
syndrome, neurogenic, 
Kaesertype(1 81400) 


LGMD2S 


4q35 


TRAPPC11 


30 


Transport protein 

nartipio pnmnloY 1 1 
pdi llUie UUI 1 ipieA 1 1 


occasional 


Young 

aril ilthnnH 
aUUlll lUUU 


Slow 


Not observed 


9-16X 




LGMD2T 


3p21 


GMPPB 


8 


GDP-mannose 
pyroptiospfiorylase B 


occasional 


Early 
childhood- 
Young 
adulthood 




Possible 




Muscular dystrophy- 
dystroglycanopathy 
(congenital with brain and 
eye anomalies), type A, 14 
(615350) 

Muscular dystrophy- 
dystroglycanopathy 
(congenital with mental 
retardation), type B, 14 
(615351) 


LGMD2U 


7p21 


ISPD 


10 


Isoprenoid synthase 
domain containing 


occasional 


Early / Late 


Rapid/ 
Moderate 


Possible 


6-50X 


Muscular dystrophy- 
dystroglycanopathy 
(congenital with brain and 
eye anomalies), type A, 7 
(614643) 


LGMD2V 


17q25.3 


GAA 


20 


Alpha-1,4-glucosidase 


occasional 


Variable 


Variable 
(Rapid to 
slow) 


Possible 


1-20X 


Glycogen storage disease 
II (232300) 


LGMD2W 


2q14 


LIMS2 


7 


Lim and senescent cell 
antigen4ike domains 2 


? 


Childhood 




Possible 







6 



Genetic basis of limb-girdle muscular dystrophies: the 2014 update 



The "dysferlinopathies" include limb-girdle muscu- 
lar dystrophy type 2B (LGMD2B) and the allelic forms 
Miyoshi myopathy (MM), which is an adult-onset dis- 
tal form, and distal myopathy with anterior tibialis on- 
set (DMAT), but varied phenotypes are observed. LG- 
MD2B affects earlier the proximal muscles of the arms 
whereas MM affects the posterior muscles of the leg. 

DYSF gene mutations are associated with heteroge- 
neous clinical pictures ranging from severe functional 
disability to mild late-onset forms (24). About 25% of 
cases are clinically misdiagnosed as having polymyosi- 
tis (25). This classification into separate phenotypes does 
not reveal true disease differences (26) and the allelic 
forms are not due to different mutations. Additional fac- 
tors (e.g., additional mutations in neuromuscular disease 
genes or sport activities that include maximal eccentric 
contractions) may worsen the disease expression of caus- 
ative mutations in dysferlinopathies (27). 

WB analysis is very useful and specific (28) when 
< 20% level of Dysferlin has been identified, although 
Dysferlin can also be increased or secondarily reduced. 
NGS -based testing is preferred due to the huge number of 
exons to be screened and the lack of mutational hot-spots. 
mRNA analysis also works from blood, albeit with some 
splice differences (29). 

LGMD2C-D-E-F 

Loss-of-function mutations in any of the genes en- 
coding the four members of the skeletal muscle sarcogly- 
can complex, alpha, beta, gamma and delta-sarcoglycan 
cause LGMD2D, 2E, 2C and 2F, respectively (30-33). 
Sarcoglycans are components of the dystrophin-complex. 
They are all N-glycosylated transmembrane proteins with 
a short intra-cellular domain, a single transmembrane re- 
gion and a large extra-cellular domain containing a clus- 
ter of conserved cysteines. 

Sarcoglycanopathies have a childhood onset, similar 
to intermediate form of Duchenne/Becker dystrophies, 
and involve both cardiac and respiratory functions. We 
consider the possibility to classify these forms apart from 
the other LGMD. 

LGMD2C - The gamma-sarcoglycan gene spans 
144kb of genomic sequence at chromosome 13ql2.12 and 
the transcript is composed of 8 exons. LGMD2C is common 
in the Maghreb and India (34) for the high allele frequency 
of 525delT and in gypsies for the C283Y allele. LGMD2C 
patients may show the absence of ijj-sarcoglycan together 
with traces of the other non-mutated sarcoglycans. 

LGMD2D - The alpha-sarcoglycan gene spans lOkb 
of genomic sequence at chromosome 17q21.33 and the 
major transcript is composed of 10 exons. The protein 
product of 387 amino acids and 50kDa was originally 



named adhalin and contains a "dystroglycan-type" cad- 
herin-like domain that is present in metazoan dystrogly- 
cans (35). 

LGMD2E - The beta-sarcoglycan gene spans 15kb 
of genomic sequence at chromosome 4ql 1 and the major 
transcript is composed of 6 exons. The protein contains of 
318 amino acids and weighs 43kDa. 

LGMD2F - Delta-sarcoglycan is by far the largest 
LGMD gene, spanning 433kb of genomic sequence at 
chromosome 5q33.3 and the major transcript is composed 
of 9 exons. Intron 2 alone spans 164kb, one the largest 
of the human genome. Delta and gamma sarcoglycan are 
homologous and of identical size (35kDa). 

LGMD2G - Mutations in titin cap (Tcap)/Telethonin 
cause LGMD2G, one of the rarest forms of LGMD (36). 
Tcap provides links to the N-terminus of titin and other Z- 
disc proteins. Patients show adolescence-onset weakness 
initially affecting the proximal pelvic muscles and then 
the distal legs with calf hypertrophy. A homozygous non- 
sense mutation in the TCAP gene has been described in 
patient a congenital muscular dystrophy. The TCAP gene 
has also been associated with cardiomyopathy (37), while 
common variants may play a role in genetic susceptibil- 
ity to dilated cardiomyopathy. Immunofluorescence and 
Western blot assays may show a Telethonin deficiency. 
Full sequencing testing may be cost-effective in all cases, 
because the gene is composed only of two small exons. 

The telethonin gene (TCAP) spans 1.2kb of genomic 
sequence at chromosome 17ql2 and the transcript is com- 
posed of 2 exons. The protein product is a 19kDa protein 
found in striated and cardiac muscle. It binds to the titin 
Z1-Z2 domains and is a substrate of titin kinase, inter- 
actions thought to be critical for sarcomere assembly. 
Only two different mutations have been described in the 
TCAP gene in Brazilian patients (36). A mutation (R87Q) 
was found in a patient with dilated cardiomyopathy (37). 
Moreover, a human muscle LIM protein (MLP) mu- 
tation (W4R) associated with dilated cardiomyopa- 
thy (DCM) results in a marked defect in Telethonin inter- 
action/localization (38). 

LGMD2H - The Tripartite-motif-containing gene 
32 (TRIM32) gene spans 14kb of genomic sequence at 
chromosome 9q33.1 and the transcript is composed of 2 
exons, with the first noncoding and the second encoding 
a 673 aa protein of 72kDa. TRIM32 is a ubiquitous E3 
ubiquitin ligase that belongs to a protein family compris- 
ing at least 70 human members sharing the tripartite mo- 
tif (TRIM). The TRIM motif includes three zinc-binding 
domains, a RING, a B-box type 1 and a B-box type 2, and 
a coiled-coil region. The protein localizes to cytoplasmic 
bodies. Although the function of TRIM32 is unknown, 
analysis of the domain structure of this protein suggests 
that it may be an E3-ubiquitin ligase (39). 



7 



Vincenzo Nigra and Marco Savarese 



LGMD2H is usually a late-onset condition charac- 
terized by proximal weakness, atrophy, and moderately 
raised levels of creatine kinase. Until 2008, the only LG- 
MD2H mutation was Asp487Asn found in Hutterite fam- 
ilies (40). Different TRIM 32 mutations were then identi- 
fied in Italian LGMD patients (41) that accounts for about 
3% of LGMD2. The D487N mutation of TRIM32 causes 
the more severe sarcotubular myopathy (STM). Recently, 
two other LGMD2H patients have been described associ- 
ated with STM morphotype (42). 

LGMD2I, LGMD2K, LGMD2M, 
LGMD2N, LGMD20, and LGMD2P 

The name dystroglycanopathy has been given to de- 
fects due to mutations in six genes (POMTl, P0MT2, 
POMGnTl, FKTN, FKRP and DAGl) (43). These varia- 
tions reduce dystroglycan glycosylation and cause a wide 
range of phenotypes ranging from mild congenital mus- 
cular dystrophies to dramatic conditions, including brain 
and eye anomalies (muscle-eye-brain disease or Walker- 
Warburg syndrome). 

LGMD2I - The fukutin-related protein gene spans 
12kb of genomic sequence at chromosome 19ql3.32 and 
the transcript is composed of 4 exons, with the first three 
noncoding. The extracellular part of the dystrophin/ 
utrophin-associated complex is also involved in congen- 
ital muscular dystrophies, as well as in LGMD2I. Fuku- 
yama-type congenital muscular dystrophy (FCMD), is 
one of the most common autosomal recessive disorders 
in Japan characterized by a congenital muscular dystro- 
phy associated with brain malformation (micropolygria) 
due to a defect in the migration of neurons caused by 
mutation in the fukutin gene at 9q31 (44). Mutations in 
the fukutin-related protein gene (FKRP) at 19ql3 cause 
a form of congenital muscular dystrophy with secondary 
laminin alpha2 deficiency and abnormal glycosylation 
of alpha-dystroglycan (45). The same gene is also in- 
volved in LGMD2I(15). 

All of these diseases are associated with changes in 
alpha-dystroglycan expression due to a glycosylation de- 
fect of alpha-dystroglycan. Dystroglycan is normally ex- 
pressed and recognized by polyclonal antibodies, but it is 
abnormally glycosylated and not recognized by monoclo- 
nal antibodies directed against certain epitopes. FKRP is 
resident in the Golgi apparatus. The P448L mutation, that 
results in CMDIC, causes a complete mislocalization of 
the protein and the alpha-dystroglycan is not processed, 
while LGMD2I mutations affect the putative active site 
of the protein or cause inefficient Golgi localization (46). 

LGMD2I mutations appear to be a relatively com- 
mon cause of LGMD, accounting for at least 10% of all 
LGMD with either severe or mild phenotypes (47, 48). 



LGMD2J - TTN is one of the most complex human 
genes. The titin gene spans 294,442 bp of genomic se- 
quence at chromosome 2q31 and the major transcript is 
composed of 363 exons. It encodes the largest protein of 
the human genome composed of 38,138 amino acids with 
a physical length of 2 microns. An 1 1-bp indel mutation 
in the last titin exon causes tibial muscular dystrophy and 
Gerull et al. (49) showed that a 2-bp insertion in exon 
326 of the TTN gene causes autosomal dominant dilated 
cardiomyopathy (CMDIG; 604145). A homozygous mu- 
tation in the C terminus of titin (FINmaj llbp deletion/ 
insertion) causes LGMD2J (50). Titin is the giant sarco- 
meric protein that forms a continuous filament system in 
the myofibrils of striated muscle, with single molecules 
spanning from the sarcomeric Z-disc to the M-band (51). 
Other "titinopathic" clinical phenotypes are tibial muscu- 
lar dystrophy (TMD, Udd myopathy) (52) or more severe 
cardiac and muscular phenotypes (53). 

CAPN3 binds M-band titin at is7 within the region 
affected by the LGMD2J mutations and shows a second- 
ary deficiency in the LGMD2J muscle (54). Interactions 
with titin may protect CAPN3 from autolytic activation 
and removal of the CAPN3 protease reverses the titin 
myopathology (55). 

The French nonsense mutation (Q33396X) located 
in Mex6, seems to cause a milder phenotype than the 
typical FINmaj mutation (51). Due to the huge gene size, 
NGS sequencing is the only possible way to study this 
gene. However, the high number of variants and polymor- 
phisms may have a confounding effect on the diagnosis. 

LGMD2K - LGMD2K is caused by hypomorphic 
missense mutations in the POMTl gene at 9q34, contain- 
ing 20 exons and spanning about 20 kb. Mutations allow- 
ing a residual enzyme activity are linked to mild forms. 
Different POMTl alleles, cause congenital muscular 
dystrophies due to defects of the dystroglycan glycosyla- 
tion (MDDGCl) and including severe forms with brain 
and eye anomalies or mental retardation (56-58). 

LGMD2L - LGMD2L is caused by mutations in the 
anoctamin-5 {AN05) gene at lip 14.3 (59). The AN05 
gene spans 90,192 bp and contains 22 exons; the cod- 
ing sequence is 2.7kb for 913 amino acids. Alternative 
gene names are TMEM16E and GDDl. Anoctamins are a 
family of calcium-activated chloride channels (60). This 
form of LGMD2 is one of the most frequent in North- 
ern Europe encompassing 10%-20% of cases (61). The 
penetrance is probably incomplete, since females are less 
frequently affected than males. The most common muta- 
tion in Northern Europe is c.191 dupA in exon 5 (62). Pa- 
tients are usually ambulant and the onset is in adulthood. 
They show asymmetric muscle involvement with preva- 
lent quadriceps atrophy and pain following exercise. CK 
levels are 5-20x. There is no evidence for contractures. 



8 



Genetic basis of limb-girdle muscular dystrophies: the 2014 update 



cardiomyopathy or respiratory involvement. LGMD2L is 
allelic with the AD gnathodiaphyseal dysphasia (63) and 
with AR distal myopathy (MMD3) (64). 

LGMD2M - This is associated with mutations in the 
fukutin gene {FKTN) at chr. 9q3 1 .2 (65). The FKTN gene 
spans 82,989 bp and contains 10 coding exons, the main 
transcript is 7.4kb encoding a protein of 413 amino ac- 
ids. Also in this case LGMD2M is a milder form caused 
by at least one hypomorphic missense mutation in a gene 
that, with both non-functional alleles, is associated with 
more severe phenotypes (66): WWS, MEB or congeni- 
tal muscular dystrophies (67). In LGMD2M the CNS is 
not affected and the intelligence is normal. Patients are 
hypotonic, may be ambulant and the onset is in early 
childhood. They show symmetric and diffuse muscle in- 
volvement that deteriorates with acute febrile illness. Im- 
provement is seen with steroids. CK levels are 10-50x. 
There is also evidence for spinal rigidity, contractures and 
cardiomyopathy and respiratory involvement. 

LGMD2N - Mutations in the P0MT2 gene, contain- 
ing 21 exons, at chr. 14q24 cause LGMD2N (68). P0MT2 
is a second O-mannosyltransferase overlapping with 
POMTl expression. P0MT2 mutations usually have a 
dramatic effect: they cause Walker- Warburg syndrome or 
muscle-eye-brain-like (69), but rarely are associated with 
LGMD (70). This may occur when the a-dystroglycan 
glycosylation is only slightly reduced. In these cases the 
mutations are usually missense and the phenotype is char- 
acterized by LGMD without brain involvement, very high 
serum CK. 

LGMD20 - It is associated with milder mutations 
in the POMGnTl gene at chr. Ip32 (71). Usually muta- 
tions in the POMGnTl gene are associated with more 
severe phenotypes than LGMD, such as Walker- Warburg 
syndrome or MEB. A homozygous hypomorphic allele of 
the POMGnTl gene was found as a 9-bp promotor dupli- 
cation (72). 

LGMD2P - LGMD2P is caused by specific changes 
of the dystroglycan (DAGl) gene itself. Recently, Camp- 
bell has reported a missense mutation in the dystroglycan 
gene in an LGMD patient with cognitive impairment (73). 
This substitution interferes with LARGE-dependent 
maturation of phosphorylated O-mannosyl glycans on 
a-dystroglycan affecting its binding to laminin. As a rule 
the dystroglycanopathies are due to mutations in genes 
involved in the glycosylation pathway of dystroglycan, 
but the dystroglycan gene is normal. 

LGMD2Q - This form of LGMD is mutation-specif- 
ic since other mutations in the Plectin (PLECl) gene at 
chrom. 8q24.3 cause epidermolysis bullosa simplex (74). 
LGMD2Q has been identified as a homozygous 9-bp 
deletion in consanguineous Turkish families (75). The 
deletion affects an AUG that is only present in a muscle- 



specific transcript Plectin If), while there are many other 
alternative first exons that are spliced to a common exon 
2. These patients produce normal skin plectin and do not 
show skin pathology. LGMD2Q patients show early-on- 
set non-progressive or slowly progressive LGMD. 

LGMD2R - Desmin is the muscle-specific member 
of the intermediate filament (IF) protein family (76). The 
desmin (DBS) gene at 2q35 contains 9 exons and spans 
about 8.4 kb. It encodes a 468-amino acid protein. Au- 
tosomal dominant mutations in the DBS gene are associ- 
ated with myofibrillar myopathy (14). The overlap with 
the DBS gene has also been claimed for LGMD IE (77). 
A homozygous splice site mutation has been identified 
in two Turkish sibs, born of consanguineous parents, in 
intron 7 of the DBS gene (c.l289-2A>G), resulting in 
the addition of 16 amino acids from residue 428. Since 
then, other mutations have been identified. The patients 
have onset in their teens or twenties of progressive 
proximal muscle weakness and non-specific atrophy af- 
fecting both the upper and lower limbs. The serum Ck 
is normal. LGMD2R patients usually show A-V con- 
duction blocks but no cardiomyopathy. 

LGMD2S - This is caused by mutation in the trans- 
port protein particle complex 11 (TRAPPCl 1) gene that 
spans 54,328 bp at chr. 4q35, the mRNA is 4.5kb and 
contains 30 exons. 

Recently, mutations in TRAPPCl 1 have been identi- 
fied in a consanguineous Syrian family with an uncharac- 
terized form of LGMD and in five Hutterite individuals 
presenting with myopathy, ID, hyperkinetic movements 
and ataxia (78). 

TRAPPCll is a transport protein particle compo- 
nent involved in anterograde membrane transport from 
the endoplasmic reticulum (ER) to the ER-to-Golgi in- 
termediate compartment (ERGIC) in mammals (79). Mu- 
tations identified so far (c.2938G>A/ p.Gly980Arg and 
c.1287h-5G>A) cause modifications in TRAPP complex 
composition, in Golgi morphology and in cell traffick- 
ing. The LGMD2S pathogenic mechanism is similar to 
that causing Danon disease, an X-linked myopathy due 
to LAMP2 mutations and affecting the secretory path- 
way (80). 

The LGMD2S phenotype ranges from a slowly pro- 
gressive LGMD with childhood onset and high CK to a 
syndrome characterized by myopathy but also neurologi- 
cal involvement (ID and ataxia). 

LGMD2T - LGMD2T is caused by milder mutations 
in the GDP-mannose pyrophosphorylase B (GMPPB) 
gene (81). The GMPPB gene is a small gene of 2,453bp 
at chr. 3p21. The mRNA is 1.7kb and contains 8 exons. 
Mutations in the GMPPB gene have been associated with 
congenital muscular dystrophies with hypoglycosylation 
of a-dystroglycan and also with LGMD only in three un- 



9 



Vincenzo Nigra and Marco Savarese 



related patients so far reported. The patients from Indian 
and Egyptian descent presented with microcephaly and 
intellectual delay. All 3 patients had increased serum cre- 
atine kinase and dystrophic findings on muscle biopsy. 
Muscle biopsy showed hypoglycosylation of DAGl. The 
English LGMD patient was a 6-year-old boy with exer- 
cise intolerance and CK = 3,000 UI. Two missense muta- 
tions were identified: pAsp27His and p.Val330Ile. 

LGMD2U - This is the form caused by some par- 
ticular alleles of the isoprenoid synthase domain contain- 
ing (ISPD) gene. The ISPD gene spans 333kb at chro- 
mosome 7p21 and contains 10 exons. ISPD mutations 
disrupt dystroglycan mannosylation and cause of Walker- 
Warburg syndrome (82, 83). Mutations in ISPD as well 
as TMEM5 genes have been associated with severe cob- 
blestone lissencephaly (84). Null alleles of ISPD produce 
Walker Warburg or cobblestone lissencephaly with brain 
vascular anomalies, but at least one milder mutation in 
one allele has been found in LGMD (68 69). We named 
this forms as LGMD2U. The association between muta- 
tions in the ISPD gene and LGMD was, however, older 
than that of forms 2P-2T, but to avoid discordant defini- 
tions among the LGMD2U should be considered as that 
caused by some alleles of ISPD. LGMD2U is progressive, 
with most cases with LGMD losing ambulation in their 
early teenage years, thus following a DMD-like path. 
In several patients, there is muscle pseudohypertrophy, 
including the tongue. Respiratory and cardiac functions 
also decline, resembling other dystroglycanopathies. 

LGMD2V - This is a proposal to name as LGMD2V 
an occasional LGMD form that derives from mild muta- 
tions of the acid alpha-glucosidase (GAA) gene (85). The 
GAA gene maps at chr 17q25.3 and comprises 20 exons 
with a protein product of 953 aa. Defects in GAA are the 
cause of glycogen storage disease type 2 (GSD2, MIM: 
232300). GSD2 is a metabolic disorder with a broad 
clinical spectrum. The severe infantile form, or Pompe 
disease, presents at birth with massive accumulation of 
glycogen in muscle, heart and liver. Late-onset Pompe 
disease may present from the second to as late as the 
seventh decade of life with progressive proximal mus- 
cle weakness primarily affecting the lower limbs, as in a 
limb-girdle muscular dystrophy. Final outcome depends 
on respiratory muscle failure. 

LGMD2W - This caused by mutations in the LIM 
and senescent cell antigen-like-containing domain protein 
2 (LIMS2/PINCH2) gene at chromosome 2ql4. The gene 
comprises 7 coding exons. It encodes a 341-aa member 
of a small family of focal adhesion proteins. The encoded 
protein has five LIM domains, each domain forming two 
zinc fingers, which permit interactions which regulate 
cell shape and migration. Patients show a childhood onset 
LGMD with macroglossia and calf enlargement. They al- 



so developed decreased ejection fraction with global left 
ventricular dysfunction in their 3rd decade, severe quadri- 
paresis and relative sparing of the face, and characteristi- 
cally a broad based triangular tongue. This form has been 
presented in a poster session at the ASHG 2013. 

The classification of LGMD is becoming too com- 
plex. We tried to reorganize the different genes so far de- 
scribed following the traditional nomenclature. However 
for the autosomal recessive forms there are few letters 
available. The next forms will be LGMD2X, LGMD2Y 
and LGMD2Z. We propose, after the LGMD2Z form, the 
acronyms LGMD2AA, LGMD2AB, LGMD2AC, etc. to 
avoid renaming consolidated definitions thereby generat- 
ing even higher confusion. 

Acknowledgements 

This study was mainly supported by grants from 
Telethon, Italy (TGM11Z06 to V.N.) and Telethon- 
UILDM (Unione Italiana Lotta alia Distrofia Musco- 
lare) (GUP 10006 and GUP11006 to V.N.). The funders 
had no role in study design, data collection and analysis, 
decision to publish, or preparation of the manuscript. 

References 

1. Nigro V, Aurino S, Piluso G. Limb girdle muscular dystrophies: 
update on genetic diagnosis and therapeutic approaches. Curr Opin 
Neurol 2011;24:429-36. 

2. Nigro V. Molecular bases of autosomal recessive limb-girdle mus- 
cular dystrophies. Acta Myol 2003;22:35-42. 

3. Nigro V, Piluso G. Next generation sequencing (NGS) strategies for 
the genetic testing of myopathies. Acta Myol 2012:31:196-200. 

4. Reilich P, Krause S, Schramm N, et al. A novel mutation in the 
myotilin gene (MYOT) causes a severe form of limb girdle muscu- 
lar dystrophy lA (LGMDIA). J Neurol 201 1;258:1437-44. 

5. Yamaoka LH, Westbrook CA, Speer MC, et al. Development of 
a microsatellite genetic map spanning 5q31-q33 and subsequent 
placement of the LGMDIA locus between D5S178 and IL9. Neu- 
romuscul Disord 1994;4:471-5. 

6. Hauser MA, Horrigan SK, Salmikangas P, et al. Myotilin is mu- 
tated in limb girdle muscular dystrophy lA. Hum Mol Genet 
2000;9:2141-7. 

7. Muchir A, Bonne G, van der Kooi AJ, et al. Identification of muta- 
tions in the gene encoding lamins AJC in autosomal dominant limb 
girdle muscular dystrophy with atrioventricular conduction distur- 
bances (LGMDIB). Hum Mol Genet 2000;9: 1453-9. 

8. Politano L, Carboni N, Madej-Pilarczyk A, et al. Advances in basic 
and clinical research in laminopathies. Acta Myol 2013;32:18-22. 

9. Gazzerro E, Bonetto A, Minetti C. Caveolinopathies: translational 
implications of caveolin-3 in skeletal and cardiac muscle disorders. 
Handb Clin Neurol 2011;101:135-42. 

10. Sarparanta J, Jonson PH, Golzio C, et al. Mutations affecting the 
cytoplasmic functions of the co-chaperone DNAJB6 cause limb- 
girdle muscular dystrophy. Nat Genet;44:450-5, Sl-2. 

1 1 . Chuang JZ, Zhou H, Zhu M, et al. Characterization of a brain-en- 



10 



Genetic basis of limb-girdle muscular dystrophies: the 2014 update 



riched chaperone, MRJ, that inhibits Huntingtin aggregation and 
toxicity independently. J Biol Chem 2002;277:19831-8. 

12. Lee HC, Cherk SW, Chan SK, et al. BAG3-related myofibrillar 
myopathy in a Chinese family. Clin Genet 2012;81:394-8. 

13. IVIessina DN, Speer MC, Pericak- Vance MA, et al. Linkage of fa- 
milial dilated cardiomyopathy with conduction defect and muscular 
dystrophy to chromosome 6q23. Am J Hum Genet 1997;61:909-17. 

14. Greenberg SA, Salajegheh M, Judge DP, et al. Etiology of limb 
girdle muscular dystrophy ID/IE determined by laser capture mi- 
crodissection proteomics. Ann Neurol 2012;71:141-5. 

15. Torella A, Fanin M, Mutarelli M, et al. Next-generation sequencing 
identifies transportin 3 as the causative gene for LGMDIF. PLoS 
One 2013;8:e63536. 

16. Peterle E, Fanin M, Semplicini C, et al. Clinical phenotype, muscle 
MRI and muscle pathology of LGMDIR J Neurol 2013;260:2033- 
41. 

17. Vieira NM, Naslavsky MS, Licinio L, et al. A defect in the RNA- 
processing protein HNRPDL causes limb-girdle muscular dystro- 
phy IG (LGMDIG). Hum Mol Genet 2014. [Epub ahead of print] 

18. Starling A, Kok F, Passos-Bueno MR, et al. A new form of auto- 
somal dominant limb-girdle muscular dystrophy (LGMDIG) with 
progressive fingers and toes flexion limitation maps to chromosome 
4p21. Eur J Hum Genet 2004;12:1033-40. 

19. Bisceglia L, Zoccolella S, Torraco A, et al. A new locus on 3p23- 
p25 for an autosomal-dominant limb-girdle muscular dystrophy, 
LGMD 1 H. Eur J Hum Genet 20 1 0; 1 8 : 636-4 1 . 

20. Fanin M, Nascimbeni AC, Fulizio L, et al. The frequency of limb 
girdle muscular dystrophy 2A in northeastern Italy. Neuromuscul 
Disord 2005;15:218-24. 

21. Pathak P, Sharma MC, Sarkar C, et al. Limb girdle muscular dys- 
trophy type 2A in India: a study based on semi-quantitative protein 
analysis, with clinical and histopathological correlation. Neurol In- 
dia 2010;58:549-54. 

22. Bashir R, Britton S, Strachan T, et al. A gene related to Caenorhab- 
ditis elegans spermatogenesis factor fer- 1 is mutated in limb-girdle 
muscular dystrophy type 2B. Nat Genet 1998;20:37-42. 

23. van der Kooi AJ, Frankhuizen WS, Barth PG, et al. Limb-girdle 
muscular dystrophy in the Netherlands: gene defect identified in 
half the families. Neurology 2007;68:2125-8. 

24. Rosales XQ, Gastier-Foster JM, Lewis S, et al. Novel diagnostic 
features of dysferlinopathies. Muscle Nerve 2010;42:14-21. 

25. Nguyen K, Bassez G, Krahn M, et al. Phenotypic study in 40 pa- 
tients with dysferlin gene mutations: high frequency of atypical 
phenotypes. Arch Neurol 2007;64: 1 176-82. 

26. Paradas C, Llauger J, Diaz-Manera J, et al. Redefining dysferlinop- 
athy phenotypes based on clinical findings and muscle imaging 
studies. Neurology;75:316-23. 

27. Weiler T, Bashir R, Anderson LV, et al. Identical mutation in pa- 
tients with limb girdle muscular dystrophy type 2B or Miyoshi 
myopathy suggests a role for modifier gene (s). Hum Mol Genet 
1999;8:871-7. 

28. Cacciottolo M, Numitone G, Aurino S, et al. Muscular dystrophy 
with marked Dysferlin deficiency is consistently caused by primary 
dysferlin gene mutations. Eur J Hum Genet 201 1;19:974-80. 

29. De Luna N, Freixas A, Gallano P, et al. Dysferlin expression in 
monocytes: a source of mRNA for mutation analysis. Neuromuscul 
Disord 2007;17:69-76. 

30. Nigro V, Piluso G, Belsito A, et al. Identification of a novel sarco- 
glycan gene at 5q33 encoding a sarcolemmal 35 kDa glycoprotein. 
Hum Mol Genet 1996;5:1179-86. 



31. Noguchi S, McNally EM, Ben Othmane K, et al. Mutations in the 
dystrophin-associated protein gamma-sarcoglycan in chromosome 
13 muscular dystrophy Science 1995;270:819-22. 

32. Lim LE, Duclos F, Bronx O, et al. Beta-sarcoglycan: characteriza- 
tion and role in limb-girdle muscular dystrophy linked to 4ql2. Nat 
Genet 1995;11:257-65. 

33. Roberds SL, Leturcq F, AUamand V, et al. Missense mutations in 
the adhalin gene linked to autosomal recessive muscular dystrophy. 
Cell 1994;78:625-33. 

34. Khadilkar SV, Singh RK, Hegde M, et al. Spectrum of mutations 
in sarcoglycan genes in the Mumbai region of western India: high 
prevalence of 525del T. Neurol India 2009;57:406-10. 

35. Piccolo F, Jeanpierre M, Leturcq F, et al. A founder mutation in the 
gamma-sarcoglycan gene of gypsies possibly predating their mi- 
gration out of India. Hum Mol Genet 1996;5:2019-22. 

36. Moreira ES, Wiltshire TJ, Faulkner G, et al. Limb-girdle muscular 
dystrophy type 2G is caused by mutations in the gene encoding the 
sarcomeric protein telethonin. Nat Genet 2000;24:163-6. 

37. Knoll R, Hoshijima M, Hoffman HM, et al. The cardiac mechanical 
stretch sensor machinery involves a Z disc complex that is defective 
in a subset of human dilated cardiomyopathy. Cell 2002; 111 :943-55. 

38. Knoll R, Kostin S, Klede S, et al. A common MLP (muscle LIM 
protein) variant is associated with cardiomyopathy. Circ Res 
2010;106:695-704. 

39. Locke M, Tinsley CL, Benson MA, et al. TRIM32 is an E3 ubiqui- 
tin ligase for dysbindin. Hum Mol Genet 2009;18:2344-58. 

40. Frosk P, Weiler T, Nylen E, et al. Limb-girdle muscular dystrophy 
type 2H associated with mutation in TRIM32, a putative E3-ubiq- 
uitin-ligase gene. Am J Hum Genet 2002;70:663-72. 

41. Saccone V, Palmieri M, Passamano L, et al. Mutations that impair 
interaction properties of TRIM32 associated with limb-girdle mus- 
cular dystrophy 2H. Hum Mutat 2008;29:240-7. 

42. Borg K, Stucka R, Locke M, et al. Intragenic deletion of TRIM32 in 
compound heterozygotes with sarcotubular myopathy/LGMD2H. 
Hum Mutat 2009;30:E83I-44. 

43. Muntoni F, Torelli S, Wells DJ, et al. Muscular dystrophies due to 
glycosylation defects: diagnosis and therapeutic strategies. Curr 
Opin Neurol;24:437-42. 

44. Kobayashi K, Nakahori Y, Miyake M, et al. An ancient retrotrans- 
posal insertion causes Fukuyama-type congenital muscular dystro- 
phy Nature 1998;394:388-92. 

45. Brockington M, Blake DJ, Prandini P, et al. Mutations in the 
fukutin-related protein gene (FKRP) cause a form of congenital 
muscular dystrophy with secondary laminin alpha2 deficiency and 
abnormal glycosylation of alpha-dystroglycan. Am J Hum Genet 
2001;69:1198-209. 

46. Esapa CT, Benson MA, Schroder JE, et al. Functional requirements 
for fukutin-related protein in the Golgi apparatus. Hum Mol Genet 
2002;11:3319-31. 

47. Stensland E, Lindal S, Jonsnjd C, et al. Prevalence, mutation spec- 
trum and phenotypic variability in Norwegian patients with Limb 
Girdle Muscular Dystrophy 21. Neuromuscul Disord 2011;21:41-6. 

48. Mercuri E, Brockington M, Straub V, et al. Phenotypic spectrum 
associated with mutations in the fukutin-related protein gene. Ann 
Neurol 2003;53:537-42. 

49. Gerull B, Gramlich M, Atherton J, et al. Mutations of TTN, encod- 
ing the giant muscle filament titin, cause familial dilated cardio- 
myopathy. Nat Genet 2002;30:201-4. 

50. Udd B, Vihola A, Sarparanta J, et al. Titinopathies and extension of 
the M-line mutation phenotype beyond distal myopathy and LG- 
MD2J. Neurology 2005;64:636-42. 



11 



Vincenzo Nigra and Marco Savarese 



51. Penisson-Besnier I, Hackman P, Suominen T, et al. Myopathies 
caused by homozygous titin mutations: limb-girdle muscular dys- 
trophy 2J and variations of phenotype. J Neurol Neurosurg Psychia- 
try 2010;81:1200-2. 

52. Udd B, Partanen J, Halonen P, et al. Tibial muscular dystrophy. Late 
adult-onset distal myopathy in 66 Finnish patients. Arch Neurol 
1993;50:604-8. 

53. Carmignac V, Salih MA, Quijano-Roy S, et al. C-terminal titin de- 
letions cause a novel early-onset myopathy with fatal cardiomyopa- 
thy. Ann Neurol 2007;61:340-51. 

54. Sarparanta J, Blandin G, Charton K, et al. Interactions with M-band 
titin and calpain 3 link myospryn (CMYA5) to tibial and limb-gir- 
dle muscular dystrophies. J Biol Chem 2010;285:30304-15. 

55. Chai'ton K, Daniele N, Vihola A, et al. Removal of the calpain 3 
protease reverses the myopathology in a mouse model for titinopa- 
thies. Hum Mol Genet 2010;19:4608-24. 

56. Beltran- Valero de Bernabe D, Currier S, Steinbrecher A, et al. Mu- 
tations in the 0-mannosyltransferase gene POMTl give rise to the 
severe neuronal migration disorder Walker-Wai'burg syndrome. Am 
J Hum Genet 2002;71:1033-43. 

57. Balci B, Uyanik G, Dincer P, et al. An autosomal recessive limb 
girdle muscular dystrophy (LGMD2) with mild mental retardation 
is allelic to Walker-Warburg syndrome (WWS) caused by a muta- 
tion in the POMTl gene. Neuromuscul Disord 2005;15:271-5. 

58. Mercuri E, Messina S, Bruno C, et al. Congenital muscular dys- 
trophies with defective glycosylation of dystroglycan: a population 
study. Neurology 2009;72:1802-9. 

59. Bolduc V, Marlow G, Boycott KM, et al. Recessive mutations in 
the putative calcium-activated chloride channel Anoctamin 5 cause 
proximal LGMD2L and distal MMD3 muscular dystrophies. Am J 
Hum Genet;86:213-21. 

60. Tian Y, Schreiber R, Kunzelmann K. Anoctamins are a family of 
Ca2-l-activated CI- channels. J Cell Sci;125:4991-8. 

61 . Witting N, Duno M, Petri H. et al. Anoctamin 5 muscular dystrophy 
in Denmark: prevalence, genotypes, phenotypes, cardiac findings, 
and muscle protein expression. J Neurol 2013;260:2084-93. 

62. Hicks D, Sarkozy A, Muelas N, et al. A founder mutation in 
Anoctamin 5 is a major cause of limb-girdle muscular dystrophy. 
Brain;134:171-82. 

63. Tsutsumi S, Kamata N, Yokes TJ. et al. The novel gene encoding 
a putative transmembrane protein is mutated in gnathodiaphyseal 
dysplasia (GDD). Am J Hum Genet 2004;74:1255-61. 

64. Penttila S, Palmio J, Suominen T, et al. Eight new mutations and the 
expanding phenotype variability in muscular dystrophy caused by 
AN05. Neurology;78:897-903. 

65. Godfrey C, Escolar D, Brockington M, et al. Fukutin gene muta- 
tions in steroid-responsive limb girdle muscular dystrophy. Ann 
Neurol 2006;60:603-10. 

66. Puckett RL, Moore SA, Winder TL, et al. Further evidence of Fu- 
kutin mutations as a cause of childhood onset limb-girdle mus- 
cular dystrophy without mental retardation. Neuromuscul Disord 
2009;19:352-6. 

67. de Bernabe DB, van Bokhoven H, van Beusekom E, et al. A ho- 
mozygous nonsense mutation in the fukutin gene causes a Walker- 
Warburg syndrome phenotype. J Med Genet 2003;40:845-8. 

68. Biancheri R, Falace A, Tessa A, et al. P0MT2 gene mutation in 



limb-girdle muscular dystrophy with inflammatory changes. Bio- 
chem Biophys Res Commun 2007;363:1033-7. 

69. Godfrey C, Clement E, Mein R, et al. Refining genotype phenotype 
correlations in muscular dystrophies with defective glycosylation 
of dystroglycan. Brain 2007;130:2725-35. 

70. Saredi S, Gibertini S, Ardissone A, et al. A fourth case of P0MT2- 
related limb girdle muscle dystrophy with mild reduction of alpha- 
dystroglycan glycosylation. Eur J Paediatr Neurol 2013. [Epub 
ahead of print] 

71. Clement EM, Godfrey C, Tan J, et al. Mild POMGnTI mutations 
underlie a novel limb-girdle muscular dystrophy variant. Arch Neu- 
rol 2008;65:137-41. 

72. Raducu M, Baets J, Fano O, et al. Promoter alteration causes tran- 
scriptional repression of the POMGNTI gene in limb-girdle mus- 
cular dystrophy type 20. Eur J Hum Genet 2012;20:945-52. 

73. Hara Y, Balci-Hayta B, Yoshida-Moiiguchi T, et al. A dystroglycan 
mutation associated with limb-girdle muscular dystrophy. N Engl J 
Med;364:939-46. 

74. Smith FJ, Eady RA, Leigh IM, et al. Plectin deficiency results in mus- 
cular dystrophy with epidemiolysis bullosa. Nat Genet 1996;13:450-7. 

75. Gundesli H, Talim B, Korkusuz P, et al. Mutation in exon If of 
PLEC, leading to disruption of plectin isoform If, causes autoso- 
mal-recessive limb-girdle muscular dystrophy. Am J Hum Gen- 
et;87:834-41. 

76. Kouloumenta A, Mavroidis M, Capetanaki Y. Proper perinuclear lo- 
calization of the TRIM-like protein myospryn requires its binding 
partner desmin. J Biol Chem 2007;282:3521 1-21. 

77. Cetin N, Balci-Hayta B, Gundesli H, et al. A novel desmin mutation 
leading to autosomal recessive limb-girdle muscular dystrophy: 
distinct histopathological outcomes compared with desminopa- 
thies. J Med Genet 2013;50:437-43. 

78. Bogershausen N, Shahrzad N, Chong JX, et al. Recessive TRAP- 
PC 1 1 mutations cause a disease spectrum of limb girdle muscular 
dystrophy and myopathy with movement disorder and intellectual 
disability Am J Hum Genet;93: 181-90. 

79. Scrivens PJ, Shahrzad N, Moores A, et al. TRAPPC2L is a novel, high- 
ly conserved TRAPP-interacting protein. Traffic 2009;10:724-36. 

80. Nishino I, Fu J, Tanji K, et al. Primary LAMP-2 deficiency causes 
X-linked vacuolar cardiomyopathy and myopathy (Danon disease). 
Nature 2000;406:906-10. 

8 1 . Carss KJ. Stevens E, Foley AR, et al. Mutations in GDP-mannose 
pyrophosphorylase B cause congenital and limb-girdle muscular 
dystrophies associated with hypoglycosylation of alpha-dystrogly- 
can. Am J Hum Genet 2013;93:29-41. 

82. Wilier T, Lee H, Lommel M, et al. ISPD loss-of-function mutations 
disrupt dystroglycan 0-mannosylation and cause Walker- Warburg 
syndrome. Nature genetics 2012;44:575-80. 

83. Roscioli T, Kamsteeg EJ, Buysse K, et al. Mutations in ISPD cause 
Walker- Warburg syndrome and defective glycosylation of alpha- 
dystroglycan. Nat Genet 2012;44:581-5. 

84. Vuillaumier-Barrot S, Bouchet-Seraphin C, Chelbi M, et al. Iden- 
tification of Mutations in TMEM5 and ISPD as a Cause of Severe 
Cobblestone Lissencephaly. Am J Hum Genet 2012;91: 1 135-43. 

85. Preisler N, Lukacs Z, Vinge L, et al. Late-onset Pompe disease is 
prevalent in unclassified limb-girdle muscular dystrophies. Molec- 
ular genetics and metabolism 2013;1 10:287-9. 



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